In an inverter device using a semiconductor switching element, a PWM signal which is a pulse string signal alternately repeating an ON signal and an OFF signal is outputted to respective gate drive circuits for upper and lower arms from a PWM, circuit, and both switching elements for upper and lower arms are turned on or off by the gate drive circuit for upper and lower arms.
Usually, for preventing both switching elements for upper and lower arms from being turned on simultaneously due to irregularities in delay time in outputting a PWM signal from the PWM circuit to the gate drive circuit, a dead time is provided to the PWM circuit for shifting turn-on timing between both switching elements for upper and lower arms. However, there is a case where simultaneous ON signals are outputted by being adversely affected by noises or the like. When the simultaneous ON signals are outputted, a power source and a ground are short-circuited to each other thus giving rise to a drawback that the switching element is broken due to a large electric current which flows at the time of short-circuiting.
In view of the above, to cope with a case where such a simultaneous ON signal is generated, there has been proposed the constitution where a simultaneous ON protection circuit is provided on a signal path between a PWM circuit and a gate drive circuit (see PTL 1, for example).